1. Field of the Invention
I have invented a new method and apparatus using an electrostatic reflector (bouncer) for injecting charged particles across a magnetic field. This method can be used to inject charged particles into a cyclotron, or possibly into a plasma confined by a magnetic field. Injection of ions into a cyclotron from an external source is advantageous since it permits uses of sources too large to fit in the center of the cyclotron, and does not require the source to operate in the strong magnetic field of the cyclotron. It also permits easy changes of the source, and of the ions to be accelerated.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97
The usual method of injection from an external source involves an axial hole in one pole of the cyclotron magnet. A. J. Cox, et al., Nucl. Instr. Methods 18-19 (1962) 25. The beam of ions passes through this hole to the midplane of the cyclotron. The beam is then deflected through an angle of 90.degree. by a reflector inclined at 45.degree. to the axis or by a helical electrostatic channel, and then begins the usual circular motion in the midplane of the cyclotron. J. L. Belmont, et al., IEEE Trans. Nucl. Sci., NS-13, No. 4 (1966) 191. The axial injection method is complicated, especially when used in a small cyclotron. Several lenses are required to transport the beam through the axial hole, and the magnetic field in the central region is non-uniform because of the axial hole. A.U. Luccio, Lawrence Radiation Laboratory Report UCRL-18016 (1968). These problems are avoided by radial injection methods.
A radial injection method which is suitable for sector focussing cyclotrons was developed at the Lebedev Institute V. A. Gladyshev, et al., Soviet Atomic Energy (Transl.) 18, No. 3 (1965) 268. The orbit center of a particle in a magnetic field follows a path of constant field, so the hill-valley magnetic field difference in a AVF cyclotron can be used to send the beam on a trochoidal path to the center region. At the center, an electrostatic channel is used to inflect the beam into a centered orbit. When the injection energy is very small, the loops in the injection beam trajectory overlap, reducing the clearance in the electrostatic channel. In another method, developed at Saclay, the ion beam was directed radially inward in the midplane across the magnetic field of the cyclotron, and the radius of curvature of the beam was increased by an electrostatic field provided by four bars, two above and two below the midplane. R. Beurtey, et al., Nucl. Instr. Methods (1965) 33:338; IEEE Trans. Nucl. Sci., NS-13, No. 4, (1966) 179; and Nucl. Instr. Methods (1967) 57:313. The bars were oriented nearly radially, with one bar of each pair positive and the other negative. The electric field of the four bars provided an effective "channel" through which the beam could be injected. When the beam reached the inner end of the bars the usual circular motion in the magnetic field began. A disadvantage of this method is the complicated and accurate shaping of the bars which is required so that the electric field will match the magnetic field profile of the cyclotron. A third method of radial injection, suitable for injection of heavy ions at relatively high energy into large cyclotrons was developed at Orsay. C. Bieth, et al., IEEE Trans. Nucl. Sci. NS-13, No. 4, (1966) 182. The ions, in low ionization states were injected in the midplane, and reached the center in about a half turn. The ions were stripped in a foil positioned to give centered orbits at a higher charge state. These and other external beam injection systems have been reviewed by Clark. D. J. Clark, Lawrence Radiation Laboratory Report UCRL-18980 (1969), and Lawrence Berkeley Laboratory Report LBL-654 (1972).